1. Field of the Invention
This invention relates to machine elements and mechanisms generally, but more particularly to small but strong plastic gear boxes with reduction drive assemblies inside.
2. Description of the Related Art
U.S. Pat. No. 5,598,746 to Chen describes a transmission assembly having a plastic box and cover employing locating posts. U.S. Pat. No. 5,737,968 to Hardey et al. discloses a gear motor assembly with a three-part molded housing having plural cylindrical connector bosses which may be ultrasonically welded together. U.S. Pat. No. 4,825,727 to Komuro relates to a speed reducer having a gear mounting plate formed with ribs for noise reduction. These three prior art devices appear to be most relevant to the gear box of the present invention, in the applicant's view.
U.S. Pat. No. 2,908,180 to Swenson reveals a gear reduction unit for a fractional horsepower motor comprising a stationary stub shaft and a rotatable work shaft with a train of intermeshing reduction gears floating free on both shafts to drive a final fixed output gear on a power shaft in the last stage. Power is received from a motor pinion driving a floating gear on a power shaft in the first or input state. U.S. Pat. No. 5,038,629 to Takimoto discloses a drive transmission mechanism having plural stages of gear reduction. Plural gears are supported by the same shaft and are rotatable relative to each other. For an example, see column 4 at lines 22-27. European Patent No. 617,213 to Masumi refers to a motorized actuator having a train of reduction gears. Plural supporting shafts each have more than one gear thereon and are able to rotate relative to one another. See column 5, line 56, through column 6, line 39. These three earlier patents appear to be the most relevant references in relation to the reduction drive assembly of the present invention, in the applicant's view.
An exemplary prior art device is illustrated in a cross-sectional view in FIG. 1. A gear box 10 has a main body 11 made of die cast zinc metal and is attached to a direct current (D.C.) motor 12 which drives a small input gear 14 held on an input shaft 16. The small input gear 14 drives a first cluster gear 18 which rotates with a first pinion gear 20 that, in turn, drives a second cluster gear 22 which rotates with a second pinion gear 24. The first cluster gear 18 and the first pinion gear 20 are mounted on a first shaft 26 while the second cluster gear 22 and the second pinion gear 24 are mounted on a second shaft 28. The first shaft 26 and the second shaft 28 are topped by spacers 30 and 32, respectively, that separate the shafts 26 and 28 from a cover 34 which is connected by screws (not shown) to the main body 11 and which is also made of the same die cast zinc metal as the main body 11. The second pinion gear 24 drives a third cluster gear 36 which rotates with a third pinion gear 38 that, in turn, drives a large output gear 40 mounted on an output shaft 42. A first collar 44 secures one end of the output shaft 42 to the main body 11 while a second collar 46 secures an opposite end of the output shaft 42 to the cover 34. A small, flat sheet of steel is rolled to form a C-shaped pin 48 that is inserted at the opposite end of the output shaft 42 in order to spin a drum or hopper 6 holding coins or tokens in a slot machine 1. The gear box 10 is fastened to the slot machine 1 through a wall 4 by a plurality of bolts 8.
Although the exemplary prior art device illustrated in FIG. 1 is made of metal, it requires screws (not shown) to fix the cover 34 to the main body 11. Thus, because the holes required for the screws weaken the solid structure of both the main body 11 and the cover 34, the gear box 10 is not as strong as it could be if there were no screw holes therethrough.
Also, because of the positioning of the various cluster gears and pinion gears on five separate shafts, the amount of force which can be transmitted from the small input gear 14 to the large output shaft 42 is limited. Thus, it remains a problem in the prior art to produce a high torque resistant and strong screwless gear box holding a reduction gear assembly inside.